1. Field of the Invention
The present invention relates to mobile communication devices and, more particularly, the present invention relates to mobile stations communicating in a mobile Internet protocol (IP) network.
2. Related Art
The Internet, as we know it today, began as a joint project between the Department of Defense's (DoD's) Advanced Research Project Agency (ARPA) and the United Kingdom's National Physics Lab (NPL) during the height of the Cold War. When planning started in 1967, the project was conceived to distribute communications and data through a dispersed network of highly interconnected network nodes with high redundancy. A decision was made, based on research at the NPL, to move data through the network using a technique called “message switching”, or packet switching as it is called today. In order to exchange data, each node was assigned a unique address in relation to the addresses assigned to all other nodes. The address scheme devised was a 32-bit number comprising a network part and a host (network node) part. By 1971, 15 nodes, mostly at universities, were connected to the ARPA network (ARPANET). They were linked for timesharing to support a variety of remote terminals and allowed data transfers between distant computers.
The early 1970s produced a number of products that would effect the development of the ARPANET. The Palo Alto Research Center (PARC), funded by Xerox Corporation, developed a graphical user interface (GUI), a computer pointing device called a mouse, and most importantly, an Ethernet protocol, for inter-connecting computers that allowed users to send and receive electronic mail and share files.
At the same time that ARPANET was being developed for institutional use, the first personal computer was introduced by Altair in 1975. Sold as a kit, it was an instant success with computer enthusiasts but its sales were limited due to the technical skill required to assemble the kit. It did, however, confirm that a market existed for a personal computer. Thus, in 1981, International Business Machines (IBM) introduced the Personal Computer (PC) which became the defacto industry standard. The IBM PC was an open architecture machine, meaning IBM published all technical details of the PC. This fact allowed low cost providers to produce PC “clones” so consumers were able to purchase personal computers at affordable prices. Low cost dial-up modems allowed PC users to download files from bulletin boards.
By the late 1980s, the ARPANET was almost 20 years old. The DoD split the ARPANET into two distinct parts for specific uses. One part was reserved for military sites (known as MILNET), while the second part of ARPANET was for civilian use. Management of the ARPANET was turned over to the National Science Foundation (NSF) with NSF regional networks forming the backbone of the re-named Internet. Commercial Internet service providers (ISPs) began offering Internet access points (APs) through which large numbers of PC users began accessing the Internet. These PCs were desktop machines whose location was not likely to change, thus creating a home network for ISPs.
As technology evolved, smaller, more powerful laptop PCs became available. Their size released them from the desktop and the office. Sales, marketing, and technical personnel could take the laptop PCs on the road while maintaining contact with the office through remote applications such as e-mail and file transfers. These laptop PCs created mobile users that wanted to access the Internet while moving between networks, thereby causing a transition from a centralized system to a distributed system. Advances in wireless technology made wireless networking possible. Using a mobile IP protocol, laptop PCs, personal digital assistants (PDAs) and mobile phones equipped for web browsing could access the Internet. Using either a static or dynamic mobile IP address assigned by their home networks, these mobile users or mobile stations accessed the Internet from any available Internet access point.
When a mobile station changes its access point from its home network to a foreign network, it does not change its IP address. Rather, an assigned IP address attaches to the mobile station as it moves from an area served by one packet data service node (PDSN) to an area served by a different PDSN. Home agents (HAs) are special servers responsible for routing data packets to absent mobile stations. The HA is informed of the absent mobile station's location when the mobile station registers with the foreign network. The server on the foreign network, the foreign agent (FA), also a PDSN, provides its IP address (care-of address) to the HA during mobile station registration. After registration, the FA is responsible for routing data packets between the mobile station and home network via the HA.
One problem with current IP networks is that there are no provisions for releasing resources between a mobile station and a PDSN if the mobile station, while in a dormant state, transitions from a first area served by a first PDSN to a second area served by a second PDSN. Currently, resources are released for a dormant mobile station after the expiration of a long timer (e.g. PPP inactivity timer). Thus, if a dormant mobile station transitions from the first area to the second area, the resources are maintained in the first area served by the first PDSN even though there is no likelihood that the dormant mobile station will become active within that first area (unless it comes back to the first area in a dormant state w/o changing the state that it maintained in the first area). Thus, system resources are wasted. A need exists, therefore, for a mechanism for releasing resources within an area served by a PDSN for a context of a mobile station that has transitioned to another area while in a dormant mode.